EP0918691A1

EP0918691A1 - Large plastic container with improved lifting ring

Info

Publication number: EP0918691A1
Application number: EP96925176A
Authority: EP
Inventors: Gerrit Jan Van Keimpema; Roger Alan Shefford
Original assignee: Koninklijke Emballage Industrie Van Leer BV
Current assignee: Greif International Holding BV
Priority date: 1996-07-26
Filing date: 1996-07-26
Publication date: 1999-06-02
Also published as: WO1998004465A1; AU737340B2; DE29614475U1; AU6535396A; ZA976601B; AR007949A1

Abstract

A plastic container comprises a container body (1), an upper end piece (3) as well as a lower end piece (2) connected to opposing ends of the container body (1) and at least one lifting ring (9) near the upper end of the container body (1) for gripping and lifting the container. The lifting ring (9) is connected to the container body (1) by means of a connecting ring (10) which, in a vertical cross section through the container axis, is running at an oblique angle between the lifting ring (9) and the container body (1). Thereby, a favourable stress distribution in the container walls due to stack loading is obtained.

Description

LARGE PLASTIC CONTAINER WITH IMPROVED LIFTING RING

The invention is related to a plastic container, comprising a container body, an upper end piece as well as a lower end piece connected to opposing ends of the container body, and at least one lifting ring near the upper end of the container body for gripping and lifting the container.

Such containers are generally known, e.g. from EP-B-515389. They are available in several sizes, ranging for instance from smaller containers of 25 litres, up to drums of about 200 litres or more. In handling of in particular the larger containers or drums, the lifting ring is of importance. For gripping this ring, several types of lifting equipment are available. As an example, the so-called parrot beak lifting equipment is often used. Also, lifting frames are known, by means of which several containers at a time can be handled.

The available lifting equipment poses a constraint with respect to the layout of the upper part of the container. In particular the distance between the higher part of the upper end piece and the lifting ring should be large enough to accommodate the upper beak of the parrot beak lifting equipment. Other lifting devices require that the upper end piece be not too high. Furthermore, the lifting ring itself should satisfy certain conditions, related to the design of its vertical face directed towards the upper end, which face is to be gripped by the upper beak of the lifting equipment, its horizontal face which is to be gripped by the lower beak, etc.

A further requirement to the present type of container is a sufficient degree of stackability. Containers with a high upper end piece generally have good stackability properties due to internal pressure build up under load. Part of the stack load is taken by the internal pressure in the container, thus relieving the container body wall and reducing buckling risks. As mentioned however, such containers with high end piece cannot be universally handled by all lifting equipment. Containers with a lower upper end in contrast do satisfy universal handling requirements with respect to all lifting equipment, but have poorer stackability properties. Under higher loads the pressure build up which can be achieved in this type of container is rather limited in particular with a view to the use of industrial pallets onto which the containers are often accommodated, such pallets being stacked one on top of another container. The pallets in question consist of often just a few, parallel spaced bottom slats which locally depress and deform the upper end piece of the container. Further pressure build up in a container is restricted when the slats of the pallet come to rest on the lifting ring.

Moreover, aside from the fact that insufficient pressure stabilisation can be achieved, in the known containers, also the contact between a slat of a pallet and the lifting ring makes the latter tilt outward which leads to buckling of the body wall of the container just below the place where such slat rests on the drum. This local buckling is a result of the couple which is exerted by the tilting lifting ring on the container body wall, in conjunction with the couple exerted thereon by the depressed upper end piece.

The object of the invention is to provide a container which can be universally handled, and which on the other hand maintains good stacking properties. This object is achieved in that the lifting ring is connected to the container body by means of a connecting ring which, in a vertical cross-section through the container axis, is running at an oblique angle between the lifting ring and the container body.

The effect of the indirect connection of the lifting ring to the container body, and at some distance offset from said body via the connecting ring, is twofold. First of all, sufficient room is available between the lifting ring and the upper end piece, such that all available lifting equipment can be applied for handling the container. It is true that, in case of a lower upper end the lifting ring is loaded sooner by the stack, for instance by a pallet, but the particular position of said lifting ring according to the invention prevents the effect of buckling from occurring.

This favourable effect is to be attributed to the fact that the outward position of the lifting ring produces, when loaded, a couple on the container body wall which counteracts the couple emanating from the loaded end piece, preferably in such a way that the couple exerted on the connection to the body wall is approximately zero. The favourable shape of the lifting ring can be improved further in case the lifting ring has an extension which extends between the lower face of the supporting flange and the connecting ring.

The lifting ring has a ring part which, in a vertical cross section, is generally extending upwardly, which ring part at its upper end carries an outwardly extending, downwardly facing supporting surface for gripping by a lifting tool. At its lower end, the ring part is connected to the connecting ring.

Furthermore, the supporting face has a recess near the ring part. This recess prevents the lower beak of the lifting equipment to cut through the supporting face. Generally, these lower beaks have a sharp front edge which might lead to incisions and finally to ruptures in the lifting ring. In the present embodiment however this sharp edge is accommodated in the recessed part of the supporting surface and thus cannot produce cutting effects.

A further improvement in the stacking performance of the container is achieved in case the container body wall and the upper end piece wall, in a vertical cross section through the container axis, merge into each other through a uniformly curved upper edge. Such uniform transition between the upper end piece and the body wall leads i.a. to a higher buckling resistance.

The upper end piece may have a substantially flat upper surface lying at a higher level than the upper edge of the lifting ring. A load exerted on such upper surface tends to concentrate near the outer circumference thereof, which leads to a better in-plane load of the body wall and less bending load thereof.

Preferably, the container body wall, in a vertical cross section through the container axis, has a body wall part which diverges from the connecting ring downwardly. This enables the body to absorb some of the load when the drum is lying on its side. Also, it allows for a greater volume inside of the drum without enlarging the overall dimensions .

Said diverging container body wall part preferably merges into an essentially cylindrical container body wall part. The outer diameter of the lifting ring is about equal to the maximal diameter of the diverging body wall part and/or the cylindrical body wall part. In this embodiment, the bending couples exerted by the lifting ring on the one hand, and the top surface of the end piece on the other hand, counteract each other in an optimal way, thus greatly reducing buckling phenomena in said body wall.

In a preferred embodiment, the connecting ring is thicker than de container body or the end piece, and is therefore less likely to break during rough handling. The inevitable curvature at the place where the ring part of the lifting ring is connected to the connecting ring, makes it more flexible, which reduces the stresses at the lifting ring.

Preferably, the upper end piece is frusto-spheπcal. The container body and/or the end pieces may be obtained by blowmoulding of thermoplastic material, or by other manufacturing methods.

The invention will further be described with reference to an embodiment shown in the figures.

Figure 1 shows a drum according to the invention in side view, and in cross-section.

Figure 2 shows an enlarged view of detail II in figure 1.

Figure 3 shows the detail according to figure 2 , in loaded condition.

Figure 4 shows a detail according to IV in figure 2. Figure 5 shows a detail according to figure 2, with definitions.

The drum shown in the figures 1 and 2 comprises a container body 1, a lower end piece 2 and an upper end piece 3- The container body 1 consists of a generally cylindrical body part k , which merges in a lower converging body part 5, and an upper converging body part 6. As shown in greater detail in figure 2, the upper converging body part 6 merges via a uniformly curved upper edge 7 into flat wall 8 of the upper end piece 3 •

At the junction between the upper end piece 3 and the container body 1, a lifting ring 9 is connected by means of connecting ring 10. As shown, the connecting ring 10 extends at an oblique angle between lifting ring 9 and container body 1. Lifting ring 9 is connected to the upper end of connecting ring 10, and extends almost vertically upwardly.

In the connecting ring 10, drainage holes 11 have been provided for draining off any fluids.

The lifting ring 9 has an outwardly extending supporting flange 12, with a downwardly directed supporting surface 13- Between the supporting surface 13 and the generally vertical ring part 21 of the lifting ring 9. a groove 14 has been provided.

The embodiment shown has a strong assembly comprising lifting ring 9 and connecting ring 10, which on the other hand also has the required flexibility in order to accommodate rough handling. Groove 14 prevents the rather sharp front edge of the beaks of a lifting device to cut into the lifting ring 9. thus ensuring safer handling characteristics: see also figure 4.

As is clear from figure 1, the lifting ring 9 is offset with respect to the upper end piece 3. in such a way that it is almost in the same vertical plane as the cylindrical body part 4 of container body 1. The important advantage of this lay-out is explained below.

When the top end piece 3 is loaded, as shown in figure 3. e.g. by the slats 16 of a pallet, the top end piece 3 is pushed downwards, thus pressurizing 26 the inner space of the drum. Thereby, the vertical wall parts of drum body 1 are partly relieved from compressive forces .

Moreover, the load of the slats 16 tends to concentrate near the outer circumference 17 of the flat wall 8 of the top end piece 3. the middle part of the flat wall 8 carrying less. Thus, a first reduction in the bending forces to which the wall of the body part 1 is exposed, is obtained.

In loaded condition, the lifting ring 9 tends to bend outside under the influence of the stack load force 24, but due to the frictional contact between the upper surface 19 and the lower surface of the slats 16, such bending outwards of the lifting ring 9 is prevented. The slats 16 exercise an inwardly directed force 23, on the lifting ring 9- These inwardly directed forces 23 lead to a couple which counteracts the couple exerted by the stack load force 24 on the top of the lifting ring, whereby a further reduction in the bending couple to which the wall of the container body 1 is exposed, is obtained. This equilibrium is further influenced by stack load force

25 on wall 8.

In summary, the wall of the container body 1 loaded to a large extent only by in-plane vertical forces, which forces can easily be resisted by such wall. The wall is only loaded by bending couples to a very limited extent, having regard to the counteracting influences as described above. A further advantage of the drum according the invention lies in the large space which is available between lifting ring 9, connecting ring 10 and the upper edge 7 ■ This space is large enough for accommodating any kind of lifting equipment. Moreover, the wall 8 of the upper end piece 3 only extends to a very limited extent above the upper surface 19 of the lifting ring 9. which further improves the possibility to handle the drum with existing lifting equipment.

Nevertheless, despite the small height of the horizontal wall 8 of the upper end piece above the lifting ring 9. and thereby despite the small contribution in the load bearing capacity due to pressure built up in the inner space of the drum, a high bearing capacity is obtained having regard to the favourable loading in the vertical wall of the container body.

In one embodiment the lifting ring and connecting ring 10 are thicker than the walls 8 and 6. This greater thickness is a result of the manufacturing process of the drum, whereby the mould part forming the end piece is displaced towards the mould part forming the drum body. In this process, a double-walled connecting ring 10 and lifting ring 9 are obtained, as is clear from the weld 15- The drum according to the invention has a weld 15 which is about perpendicular to the lifting load which is a favourable direction. Thus , an improvement is obtained here in comparison to prior art container, the latter having a similar weld which however is exposed to shear loads. Furthermore, the transition from body wall 8 to edge 7 is smooth, which reduces the risk of environmental stress cracking.

Figure 5 finally shows a number of dimensions which are important design requirements for the lifting ring and upper end. The generally vertical face 22 of ring part 21 is to be gripped by the upper beak of the lifting equipment. This is only possible in case the distance a between said face 22 and the opposite, upwardly extending upper end 8 is large enough. Moreover, the height b of said face should be large enough to provide sufficient room for the upper beak.

The lower supporting face 13 is to be gripped by the lower beak; it should be wide enough to ensure a reliable gripping action; on the other hand, the overall width e of the lifting ring 9 should be limited. Also, the distance c between the upper surface 19 of the lifting ring 9, and the upper surface 8 of the upper end, as well as the height d between the upper surface 19 and the supporting surface 13 should be limited.

Moreover, the overall height b of the lifting ring 9 itself should have a prescribed value.

Claims

C l a i m s

1. Plastic container, comprising a container body (1), an upper end piece (3) as well as a lower end piece (2) connected to opposing ends of the container body (1), and at least one lifting ring (9) near the upper end of the container body (1) for gripping and lifting the container characterised in that the lifting ring (9) is connected to the container body (1) by means of a connecting ring (10) which, in a vertical cross-section through the container axis, is running at an oblique angle between the lifting ring (9) and the container body (1).

2. Container according to claim 1, wherein the lifting ring (9) has an extension (27) which extends between the lower face (13) of the supporting flange (12) and the connecting ring (10).

3. Container according to claim 1 or 2, wherein the lifting ring (9) has a ring part (21) which, in a vertical cross section, is generally extending upwardly, which ring part (21) at its upper end carries an outwardly extending, downwardly facing supporting surface (13) for gripping by a lifting tool.

4. Container according to claim 3. wherein the ring part (21) at its lower end is connected to the connecting ring (10).

5. Container according to claim or 4, wherein the supporting face (13) has a recess (14) near the ring part (21).

6. Container according to any of the preceding claims, wherein the container body wall and the upper end piece wall, in a vertical cross section through the container axis, merge into each other through a uniformly curved upper edge (7) •

7. Container according to claim 6, wherein the upper end piece (3) has a substantially flat upper surface (8) lying at a higher level than the upper edge (19) of the lifting ring (9).

8. Container according to any of the preceding claims, wherein the container body wall, in a vertical cross section through the container axis, has a body wall part (6) which diverges from the connecting ring (10) downwardly.

9. Container according to claim 8, wherein the diverging container body wall part (6) merges into an essentially cylindrical container body wall part (4).

10. Container according to claim 8 or 9, wherein the outer diameter of the lifting ring (9) is about equal to the maximal diameter of the diverging body wall part (5, 6) and/or the cylindrical body wall part (4) .

11. Container according to any of the preceding claims, wherein the connecting ring (10) has drain holes (11).

12. Container according to any of the preceding claims, wherein the upper end piece (3) is frusto-spherical.